1. Field of the Invention
Injection nozzles are essential components of self-igniting internal combustion engines. Among their tasks are metered injection, fuel preparation, shaping of the course of injection, and sealing off from the combustion chamber. In common rail Diesel injection systems, along with the main injection a preinjection is effected, which makes it possible to reduce exhaust emissions and noise. The present invention, however, relates not only to fuel injection nozzles but also to all types of nozzles and metering valves.
2. Prior Art
German Patent Disclosure DE 196 34 933 relates to a fuel injection valve for internal combustion engines, with a valve member that is axially displaceable in a bore of a valve body. On its end toward the combustion chamber of the engine, the valve member has a conical valve sealing face, with which it cooperates with a conical valve seat face on the closed end, toward the combustion chamber, of the bore of the valve body. The conical valve sealing face of the valve member is divided into two regions of different cone angles. At the transition between the two regions, a valve sealing edge is formed. The fuel injection valve also has at least one injection opening, which is located in the region adjoining the sealing edge downstream thereof. Finally, between the valve sealing face regions that each have a different cone angle, a shoulder is provided, which has advantages in terms of the accuracy of metering the injection quantity.
The metering of the injection quantity by a fuel injection nozzle varies over its service life, because of wear. Especially in common rail injectors, the position of the valve sealing face, that is, the face with which the valve needle tip comes to rest on the conical inner wall of the valve body, in the closing position of the valve. Because of wear, the valve sealing face can “wander” toward either a larger or a smaller diameter of the conical valve needle tip. Consequently in the closing position of the valve, the valve needle comes to rest at a higher point on the inner wall of the valve body, relative to the valve body. The result is an altered injection course. Particularly in common rail injection nozzles, this means that with an increasing number of load changes (number of alternating load stresses), the preinjection quantity becomes smaller and finally vanishes entirely.